Abstract
Fungal meroterpenoids are important bioactive natural products. Their biosynthetic machineries are highly diverse, and reconstitutions lead to the production of unnatural meroterpenoids. In this study, heterologous gene expression in Aspergillus oryzae and in vitro assays elucidated the biosynthetic pathway of the orthoester-containing fungal meroterpenoid austalide F. Remarkably, the α-ketoglutarate-dependent oxygenase AstB produces the hemiacetal intermediate, and the methyltransferase AstL transfers a methyl group on it to construct the orthoester functionality. This study presents the extraordinary orthoester biosynthetic machinery and provides valuable insights into the creation of unnatural novel bioactive meroterpenoids through engineered biosynthesis. This article is part of the theme issue 'Reactivity and mechanism in chemical and synthetic biology'.